Induced pluripotent stem cells (iPSCs) from patients with kidney disease have significant potential for patient-specific disease modeling and immunocompatible tissue replacement therapy. The applicant, Dr. Benjamin Freedman, has performed pioneering studies in these areas in the laboratory of the mentor, Dr. Joseph Bonventre. This application's goal is to further expand the candidate's expertise and findings in this novel research area into a well-rounded, independent research program. Dr. Freedman recently led research establishing iPSC models for polycystic kidney disease (PKD), a leading cause of kidney failure. PKD is caused by mutations in polycystin-1 (PC1), PC2, and fibrocystin/polyductin (FPC), which interact at the primary cilium. Reduced ciliary PC2 was found to be a common feature in ADPKD iPSCs and descendant epithelial cells and hepatoblasts, when compared to equivalent cultures from healthy or ARPKD patients. Overexpression of wild-type PC1 rescued PC2 localization to cilia, suggesting a possible therapeutic approach. Protocols have recently been developed in our laboratory for directed differentiation of iPSCs into kidney progenitor-like cells (KPCs) expressing markers of the renal lineage. Utilizing existing and innovative PKD iPSC lines, Dr. Freedman will test the hypothesis that PKD disease mutations result in dedifferentiation and cell cycle phenotypes in 2D culture and aberrant cystogenesis in 3D culture. To extend this work in vivo, iPSC-derived KPCs will be implanted into immunodeficient mice to form tissue growths, which will be carefully examined for histological and immunohistochemical evidence supporting kidney differentiation and PKD-specific cystogenesis. These experiments will advance our understanding of PKD pathogenesis, produce innovative cell lines and methodologies for future research, and expand Dr. Freedman's technical repertoire to include new skills of genome modification, 3D culture, and in vivo differentiation. Dr. Freedman will devote 100 % of his time to research under this award and Brigham and Women's Hospital will promote him to a faculty position. Dr. Bonventre will continue to mentor Dr. Freedman on a daily basis, providing office and bench space to him and his research assistants and access to all of the Bonventre facilities including all the necessary equipment to complete these studies. Dr. Freedman will be co-mentored by three renowned experts in PKD pathophysiology and treatment at Harvard: Dr. Jing Zhou, Dr. Friedhelm Hildebrandt, and Dr. Theodore Steinman. The mentor and co-mentors will meet to evaluate Dr. Freedman's progress every six months. Dr. Freedman will supplement his education with 1) weekly meetings and seminars devoted to stem cells, PKD, and kidney physiology, 2) national stem cell and nephrology conferences, and 3) responsible conduct of research courses. He is expected to produce first author manuscripts on an annual basis during the award period and will be competitive for independent research awards by the end of the third year.